The so-called ADM (acronym of <<Aerosol Deposition Method>>) technique has several advantages in forming deposits of ceramics or other fragile materials.
The article of Jun Akedo, <<Room Temperature Impact Consolidation of Fine Ceramic Powder by Aerosol Deposition Method and Applications to Microdevices>>, Journal of Thermal Spray Technology, Vol. 17(2), June 2008, pp. 181-198, describes this method and the contemplated applications.
FIG. 1 illustrates a known device allowing application of this technique.
The device comprises an aerosol chamber 10 which contains a ceramic powder 1.
The aerosol chamber 10 is connected to a gas supply device 20 which allows injection of said gas into the chamber 10 in order to mix it with the ceramic powder 1.
Moreover, a vibratory device (not shown) is configured so as to cause vibration of the chamber 10 containing the mixture of gas and of ceramic powder suitable for generating an aerosol.
Said aerosol is then injected into a deposition chamber 30 via a nozzle 31.
Optionally, one or more filters 40 may be placed on the path of the aerosol between the chamber 10 where it is generated and the deposition chamber 30, so as to retain or select the grains having the desired grain size.
Inside the deposition chamber 30, a substrate 3 is laid out onto which the ceramic powder has to be deposited.
The substrate 3 is maintained by a support 32 which is translationally moveable in the chamber, thereby allowing displacement of the substrate 3 relatively to the nozzle 31.
During the injection of the aerosol, vacuum is applied in the deposition chamber 30 by means of a pumping system 50.
The ceramic powder grains contained in the aerosol are accelerated through the nozzle 31 and cross the space separating the outlet of the nozzle 31 from the substrate 3 with high kinetic energy (the flow of the aerosol is illustrated by the mark 1′).
Upon entering into contact with the substrate 3, the powder grains fragment and locally form a cohesive deposit.
This cohesion is directly induced by the energy released upon the impact without it being necessary to then proceed with sintering.
Thus, by displacing the substrate 3 relatively to the nozzle 31, it is possible to form a ceramic deposit at the surface of the substrate 3 without any heat treatment being required.
This method has multiple advantages.
On the one hand, the obtained fragile material deposit has sufficient mechanical cohesion so as not to require sintering, as opposed to known methods for example applying ceramic powders which require sintering at a high temperature for giving the deposit the required mechanical properties (hardness, cohesion).
As the method is applied at room temperature, the deposition of a fragile material may be carried out on any type of substrate, including substrates which do not withstand a high temperature and which therefore cannot be used in methods involving high temperature sintering.
The applications of this method are therefore very numerous.
Known devices give the possibility of obtaining continuous deposits at the surface of the substrate, i.e. a deposit for which the surface is in one piece and which most often has rectilinear edges.
Indeed, the surface of the substrate onto which the deposit is deposited is generally planar, and the devices generally provide a relative displacement of the substrate relatively to the nozzle along one or two orthogonal axes in a plane perpendicular to the direction of the aerosol flow 1′.
Reference may for example be made to document U.S. Pat. No. 6,531,187.
In particular, the deposition is accomplished by sweeping with the nozzle the surface of the substrate, the nozzle travelling along successive parallel lines until coverage of the desired surface.
This deposition method is for example described in document US 2011/0070359.
Document US 2006/0222862, as for it, contemplates the making of a deposit at the surface of a raised and recessed object, the nozzle then being placed at the end of an arm controlled by a computer which allows the surface of the object to be followed while maintaining the nozzle at a constant distance from the surface.
This is also a deposition carried out continuously over the surface of the object.
However, the problem is posed of depositing a discontinuous deposit at the surface of the substrate, i.e. a deposit distributed according to a predefined pattern (for example, a spiral) and/or consisting of several distinct patterns (for example, several discs) on the surface of the substrate.
Placing a mask for which the apertures define the desired pattern between the nozzle and the substrate is known, notably by the article mentioned above and by document U.S. Pat. No. 7,479,464.
However, the use of such a mask is delicate since, on the one hand, the edges of the apertures of said mask may divert the flow of the aerosol, which may lead to erosion of the substrate rather than to the formation of the deposit.
This imposes a very fine adjustment of the parameters of the flow of the aerosol, notably the negative pressure in the deposition chamber, the angle of incidence of the flow of the aerosol.
On the other hand, the known masks do not give the possibility of producing deposits according to more complex patterns, such as a spiral for example.
Moreover, if it is desired to form a pattern for which the dimensions in a plane parallel to the surface of the substrate vary according to the thickness (for example, a pattern, for which the section in a plane perpendicular to the surface of the substrate is trapezoidal or triangular), it is necessary to successively use several masks, the apertures of which are increasingly narrower.
Taking into account the fineness of the obtained deposits, the handling of these different masks would be particularly complicated for obtaining the desired section.
In any case, this masking technique seems to be particularly difficult to apply on a substrate for which the surface is not planar.
An object of the invention is therefore to provide a method for depositing a powder of a fragile material on a substrate which allows formation of a deposit consisting of one or more predefined patterns, without resorting to a mask, which would impose additional costs and manufacturing delays.
Another object of the invention is to propose a method for depositing a powder of a fragile material on a substrate which allows formation of a deposit, the dimensions of which vary over the thickness of the deposit, without resorting to several successive masks, for which the manufacturing costs are high and the lifetimes are short.
In other words, an object of the invention is to provide more flexibility as regards the geometry of the deposit than present methods using masks.